As mobile device technology continues to develop and demand therefor continues to increase, demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, have long cycle lifespan, and have a low self-discharge rate, are commercially available and widely used.
In addition, as recent interest in environmental problems is increasing, research into electric vehicles (EVs), hybrid electric vehicles (HEVs), and the like that can replace vehicles using fossil fuels, such as gasoline vehicles, diesel vehicles, and the like, which are one of the main causes behind air pollution, is underway. As a power source of EVs, HEVs, and the like, a nickel-metal hydride (Ni-MH) secondary battery is mainly used. However, research into lithium secondary batteries having high energy density, high discharge voltage, and high output stability is actively carried out and some of the lithium secondary batteries are commercially available.
A lithium secondary battery has a structure in which an electrode assembly, which includes: a cathode prepared by coating a cathode active material on a cathode current collector; an anode prepared by coating an anode active material on an anode current collector; and a porous separator disposed between the cathode and the anode, is impregnated with a lithium salt-containing non-aqueous electrolyte.
Such lithium secondary batteries require a certain level or higher of porosity of an electrode in consideration of ionic conductivity of active materials.
However, excess reduction in porosity of an electrode occurs in a process of preparing an electrode slurry including an electrode active material and, consequently, rapid decrease in C-rate may be caused.
Secondary batteries require a certain level or higher of C-rate according to individual applications and, in particular, secondary batteries for power tools which require high power or secondary batteries for EVs and HEVs require much higher C-rate.
Therefore, there is an urgent need to develop a technology that may address the above-described problems.